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Effects of fragmentation on pollination and regeneration of South American Polylepis australis woodlands
Dissertation (kumulativ)
Zur Erlangung des akademischen Grades
doctor rerum naturalium (Dr. rer. nat.)
vorgelegt der
Mathematisch-Naturwissenschaftlich-Technischen Fakultät
(mathematisch-naturwissenschaftlicher Bereich)
der Martin-Luther-Universität Halle-Wittenberg
von
Diplom-Biologin Peggy Seltmann
geboren am 25.02.1976 in Erlabrunn
Gutachterin bzw. Gutachter:
1. Prof. Dr. rer. nat. habil. Isabell Hensen
2. Prof. Dr. rer. nat. habil. H. Bruelheide
3. Prof. Dr. rer. nat. habil. Markus Fischer
Halle (Saale), 2006
urn:nbn:de:gbv:3-000010852[http://nbn-resolving.de/urn/resolver.pl?urn=nbn%3Ade%3Agbv%3A3-000010852]
Table of contents 1
TABLE OF CONTENTS
CHAPTER I: EFFECTS OF FRAGMENTATION ON POLLINATION AND REGENERATION OF SOUTH AMERICAN POLYLEPIS AUSTRALIS WOODLANDS – INTRODUCTION AND OVERVIEW Forest fragmentation and consequences ……………………………. 3
Polylepis forests ………………………..……………………………. 5
Study species and area …………………………………………….… 7
Aims and questions ………………..……………………………. 10
Survey of methods and results, and first conclusions ………………. 11
References ……………………………………………………………… 13
CHAPTER II: MATING SYSTEM, OUTCROSSING DISTANCE EFFECTS AND POLLEN AVAILABILITY IN THE WIND-POLLINATED TREELINE SPECIES POLYLEPIS AUSTRALIS Abstract ……………………………………………………………… 17
CHAPTER III: BIPARENTAL INBREEDING DEPRESSION, GENETIC RELATEDNESS AND PROGENY VIGOUR IN A WIND-POLLINATED TREELINE SPECIES IN ARGENTINA Abstract ……………………………………………………………… 18
CHAPTER IV: WOODLAND FRAGMENT SIZE, POLLINATION EFFICIENCY AND REPRODUCTIVE SUCCESS IN NATURAL POPULATIONS OF WIND-POLLINATED POLYLEPIS AUSTRALIS (ROSACEAE) TREES Abstract ……………………………………………………………… 19
CHAPTER V: VARIATION IN SEED MASS AND ITS EFFECTS ON GERMINATION IN POLYLEPIS AUSTRALIS: IMPLICATIONS FOR SEED COLLECTION
Table of contents 2
Abstract ……………………………………………………..………. 20
CHAPTER VI: COMPREHENSIVE CONCLUSIONS …………………… 21
CHAPTER VII: ANHANG Erklärung über den persönlichen Anteil an den Publikationen ……….... 24
Curriculum vitae …………………………………………….……..….. 27
Publikationsliste ……………………………..………………………… 29
Eigenständigkeitserklärung ………………………………………… 30
Effects of fragmentation on pollination and regeneration of Polylepis australis 3
CHAPTER I
EFFECTS OF FRAGMENTATION ON POLLINATION AND REGENERATION OF SOUTH AMERICAN POLYLEPIS AUSTRALIS WOODLANDS – GENERAL INTRODUCTION AND OVERVIEW
Forest fragmentation and consequences Worldwide, large areas of continuous forests are rapidly becoming fragmented
as a result of human activities. Across the globe, forests have been cut for reasons of
wood production, burnt or clear-cut to produce grasslands for livestock, agricultural
lands or urban areas, changing in this way the face of many forest landscapes
(Ellenberg, 1979; Spies, 1998). Remaining forests are often highly fragmented and
their defining characteristics modified. These transformations are connected with a
loss of ecosystem functions formerly provided by the original closed forests. Forests
are important, for example, for controlling soil erosion, increasing water catchment
capacity of the area and providing habitat for wildlife (Hunter, 1990; Fjeldså &
Kessler, 1996; Spies, 1998).
As documented by several studies, the restriction of formerly common tree
species to small and isolated fragments may subsequently lead to increased
inbreeding depression because of cumulative effects of genetic drift (e.g. Fischer &
Matthies, 1997; Gigord et al., 1998; Hedrick & Kalinowski, 2000; Glémin et al., 2001).
While inbreeding usually refers to the mating of closely related individuals, inbreeding
depression is defined as reduced fitness of the offspring of related mates compared
to the offspring of randomly mated individuals (Hedrick & Kalinowski, 2000). Genetic
drift in small populations can lead to decreased fitness in all, or nearly all, of their
Effects of fragmentation on pollination and regeneration of Polylepis australis 4
individuals compared to larger populations (Hedrick & Kalinowski, 2000). In
accordance, the potential for inbreeding depression has been demonstrated in
various animal-pollinated species (e.g. Aizen & Feinsinger, 1994; Moran-Palma &
Snow, 1997; Fischer & Matthies, 1997; Larson & Barrett, 2000; Garcia Collevatti et
al., 2001; Stacy, 2001), and for a number of conifers (e.g. Krakowski et al., 2003;
Wang et al., 2004). However, very little is known about biparental inbreeding
depression in wind-pollinated woody angiosperms.
Furthermore, both fragmentation of woodlands and small fragment size may
reduce pollen availability and thus, limit reproduction. While preliminary experimental
evidence suggests that reproduction in populations of wind-pollinated trees is pollen-
limited under certain conditions (e.g. Perry & Knowles, 1990; Allison, 1990; Holm,
1994; Knapp et al., 2001), a consensus on this issue has yet to be achieved (studies
in contrast: e.g. Dow & Ashley, 1998; Streiff et al., 1999).
In addition, abundant theory postulates a reduction in gene flow among
fragmented populations of many species, including numerous maladaptive
consequences which can follow from genetic isolation (Ellstrand & Elam, 1993;
Smouse & Sork, 2004). In contrast to the general assumption of extensive pollen flow
in wind-pollinated trees (e.g. Adams & Burczyk, 2000; Hamrick & Nason, 2000),
recent studies by Knapp et al. (2001), Sork et al. (2002) and Satake & Iwasa (2002)
have lead to the conclusion that short-distance dispersal of pollen tends to be
common, and that increased fragmentation could ultimately result in reproductive
failure in wind-pollinated tree species (Koenig & Ashley, 2003).
Thus, for successful conservation efforts of remaining fragments it is crucial to
gather knowledge both on reproductive processes and on gene transfer of the
involved tree species. This applies particularly to highly fragmented ecosystems
where it is indispensable to assess whether progressive habitat degradation, size
reduction and increasing isolation actually accelerate further declines in populations.
A substantiated knowledge on gene transfer is especially important because gene
flow is one of the key factors determining species responses to fragmentation
(Burczyk et al., 2004).
The next chapters focus on the genus Polylepis with the intention of highlighting
its mating system, possible scenarios of gene transfer and reproductive responses to
forest fragmentation.
Effects of fragmentation on pollination and regeneration of Polylepis australis 5
Polylepis forests The genus Polylepis R. & P. (Rosaceae, Sanguisorbeae) includes about 28
wind-pollinated species of short to tall trees and shrubs of usually gnarled shape. The
bark of Polylepis consists of numerous
layers of thin, dark red exfoliating sheets as
a protection against low temperatures
(Simpson, 1979; Fjeldså & Kessler, 1996).
While all species of Polylepis have
compound imparipinnate leaves, the number
of pairs of leaflets varies within and among
species. The genus is distributed along the
South American Andes (Venezuela,
Colombia, Ecuador, Peru, Bolivia, Chile and
North-Argentina) and in the Córdoba
mountains, Argentina (Simpson, 1979;
Simpson, 1986; Kessler, 1995a; Kessler,
1995b; Schmidt-Lebuhn et al., submitted;
Fig.1). Some of the species grow in the area
of the tropical upper mountain forest, the
others in isolated stands far above a closed
treeline up to an altitude of 5.200m a.s.l.
where they form the world´s highest
woodlands (Troll, 1959).
Figure 1. Approximate distribution of Polylepis (from: Schmidt-Lebuhn, 2005)
Once assumed to be patchy by nature, Polylepis forests are now recognized to
be highly endangered due to human impact (Fjeldså, 2002; Kessler, 2002; Purcell et
al., 2004; Renison et al., 2006). Exploitation of South American high mountains since
Incan times has greatly reduced forest areas. Recent forests occupy only about one
percent of their original area in the eastern Bolivian Andes and about three percent in
Peru (Fjeldså & Kessler, 1996; Purcell et al., 2004). In other countries, the extent of
Polylepis forest loss is not quantified but likely to be equally high (Renison et al.,
2006).
Effects of fragmentation on pollination and regeneration of Polylepis australis 6
In consequence, several recent studies have investigated the effects of
anthropogenic activities on Polylepis forests (e.g. Acosta, 1986; Hensen, 2002;
Renison et al., 2002; Teich et al., 2005; Renison et al., 2006). Much effort has been
done to achieve a substantiated knowledge on successful reforestation of the
endangered habitats (Kopta, 1985; Brandbyge & Holm-Nielsen, 1987; Renison &
Cingolani, 1998; Ibisch, 2002; Renison & Cingolani, 2002; Renison et al., 2002;
Renison et al., 2005). However, reforestation may be hampered due to the low seed
viability or/and low germination rates reported for several Polylepis species (Pretell
Chiclote et al., 1985; Brandbyge & Holm-Nielsen, 1987; Reynel & Leon, 1990;
Hensen, 1994; Renison et al., 2004). In this context, Renison et al. (2004)
investigated the effects of habitat degradation on P. australis and detected both a
positive relationship between seed viability and soil conditions, and a negative
correlation with soil erosion. In addition, reforestation success may be negatively
affected by the vigour of the seedlings. Indeed, Renison et al. (2005) found that
seedling growth during their first five years was faster when seedlings derived from
seeds collected in a large, well-preserved forest than from seeds collected in smaller
forest fragments.
However, despite substantial evidence of the negative impact of fragmentation
and habitat degradation on Polylepis reproduction, no specific studies exist which
have investigated the mating system and pollination biology of Polylepis species,
and, based on that, pollination-based responses to fragmentation.
Well-founded knowledge of the mating system of a species is an essential
prerequisite for evaluating the dependence of seed production and progeny attributes
on pollination rate and type, and may subsequently lead to a greater understanding
of the mechanisms of gene flow within and between populations (Barrett & Eckert,
1990).
In the following, defining characteristics of Polylepis australis as representative
for the genus are discussed in detail.
Effects of fragmentation on pollination and regeneration of Polylepis australis 7
Study species and area
Figure 2. Collection localities of Polylepis Figure 3. Polylepis australis Bitter. (A) branch australis Bitter (from: Simpson, 1997) (B) flower C. fruit (from: Simpson, 1979).
Polylepis australis Bitter is the southernmost Polylepis species, endemic to
Argentina where it occurs in the mountains of the provinces of Jujuy, Salta,
Catamarca, Tucumán, Córdoba and San Luis (Simpson, 1979; Fig. 2). It is the only
native species that forms forests in the higher mountains of Central Argentina
(Renison et al., 2004).
The species comprises shrubs and trees that are 1.5 to 14m in height (Simpson,
1986). Its racemiform pendulous inflorescences are 1.8 to 7.3cm long catkins that are
produced annually. They may carry up to twelve perfect wind-pollinated flowers with
typical anemophilous features such as reduced inconspicuous corollas, protogyny
and a large stigmatic surface area (Fig. 3, 4). Each flower is 0.7-1.0cm in diameter
with three or four green sepals and 8–16 stamens (Simpson, 1979; Fig. 3, 4). Anthers
are red, conspicuous and open by longitudinal slits (Fig. 4). The stigma is uniformly
expanded and fimbrillate (Simpson, 1986; Fig. 3, 4). Self-pollination is precluded by
protogyny, i.e. temporal staggering of sexual maturity within the flower with stigmas
being receptive only before the anthers open. Polylepis australis pollen is arranged in
monads, more or less spheroidal in shape, 58–76µm wide and 3-colporate (Simpson,
1986; Fig. 5). Flowers generally develop one ovule (with only few exceptions where
Effects of fragmentation on pollination and regeneration of Polylepis australis 8
two are formed, personal observation), and fruits are mostly single seeded nutlets
that are enclosed in a turbinate and winged receptaculum (Fig. 3).
Figure 5. Polylepis australis pollen grains (20x), Photo: Andrea Cocucci.
Investigations were carried out in the Córdoba mountains, Central Argentina (31º
34’ S, 64º 50’ W). The mean annual temperature is 8°C, and there is no frost-free
period. Mean annual precipitation is 840mm with most rainfall concentrated in the
warmer months between October and April (Cabido et al., 1987). Woodlands are
dominated almost exclusively by P. australis trees (Cingolani et al., 2004) whose
stands can be found between 900 and 2.884m a.s.l.
Human intervention and forest fragmentation probably started 8000 years ago
when the first Amerindians settled in the area and started using burning techniques
for hunting (Berberían, 1999; Pastor, 2000). After European settlement, forests
further declined and degradation proceeded due to fire, introduction of cattle grazing
and utilization of timber and firewood (Cabido & Acosta, 1985; Kopta, 1999;
Cingolani et al., 2004; Renison et al., 2004).
Effects of fragmentation on pollination and regeneration of Polylepis australis 9
A B
C
Figure 4. Polylepis australis Bitter. (A) Inflorescence with flowers in the male phase (anthers opened); (B) Longitudinal section of a flower in the male phase; (C) Branch with inflorescence and young infructescences. Photos: A. Cocucci.
Effects of fragmentation on pollination and regeneration of Polylepis australis 10
Aims and questions current investigation is not only to improve the knowledge
on th
• Is self-pollination possible? Are there differences in the reproductive output of
Is there a relationship between genetic similarity and geographic distance in P.
• How are the relationships between woodland fragment size, natural pollination
• To what extent does the seed mass affect P. australis seed germination? Does
The central aim of the
e pollination biology and the mating system of Polylepis but also, moreover, to
assess pollination-based responses of Polylepis to fragmentation. An additional goal
was to contribute to the knowledge on possibilities for successful reforestation. Thus,
Polylepis australis was used to answer the following main questions:
self- and cross-pollinated flowers? Does the distance between mates affect
seed mass and germination? Are there any indications for pollen limitation and
for pollen longevity being a limiting factor in the pollination process? (CHAPTER
II)
•
australis woodland fragments? Do outcrossing distances influence genetic
variability and vigour of the progeny? What scenarios of gene transfer are
most likely to be occurring in P. australis woodland fragments at the current
fragmentation level? (CHAPTER III)
and reproductive success in P. australis woodland fragments? (CHAPTER IV)
the knowledge on this relationship contribute to successful reforestation?
(CHAPTER V)
Effects of fragmentation on pollination and regeneration of Polylepis australis 11
Survey of methods and results, and first conclusions CHAPTER II…deals with effects of hand-selfing, varying outcrossing distances of
up to 30km and pollen addition on seed mass and seed germination of Polylepis
australis. In addition, pollen germination on the stigma and pollen tube growth were
investigated to determine compatibility resulting from selfing and outcrossing, as well
as pollen longevity.
To test for self-fertilization and the effect of outcrossing distances, flowers of P.
australis individuals equally distributed between two woodland fragments were hand-
pollinated with self-pollen and with cross-pollen belonging to different distance-
classes. Pollen addition experiments were performed in four woodland fragments
differing in size.
The results suggest a potential for inbreeding depression through selfing and
crosses within woodland fragments. However, the results also indicate that pollen
flow between P. australis woodland fragments is still effective at the current
fragmentation level. In coincidence, results suggest that P. australis pollen grains
remain viable long enough to complete the pollination process even over longer
distances. Furthermore, even in case of relatively small woodland fragments, pollen
availability does not seem to limit reproductive success.
CHAPTER III…focuses on the relationships between parental genetic similarity,
outcrossing distances and progeny vigour as measured by N metabolism capacity of
the seedlings. Genetic variability and vigour of the resulting progeny were contrasted
with progeny from open pollinated flowers.
Seedlings resulting from seeds that had been obtained by crosses with pollen
belonging to different distance-classes (chapter II) were used for the evaluation of the
N metabolism capacity. All remaining seedlings served as plant material for genetic
analysis (RAPD-PCR). Leaf tissue from focal females and from pollen donors from
each of the respective distance classes was used to assess parental genetic
similarity.
The study revealed a continuous decrease of parental genetic similarity with
spatial distance among mates and an increase of N metabolism capacity with
increasing distances of pollen provenance. It can be concluded that genetic similarity
between focal females and pollen donors can be seen as an underlying factor for
biparental inbreeding depression in the study species. Consequently, this is the first
Effects of fragmentation on pollination and regeneration of Polylepis australis 12
study providing evidence of biparental inbreeding in a wind-pollinated angiosperm
tree.
However, the results confirm and underline the assumption of fragment
connectivity at the current fragmentation level as derived from chapter II. Effective
long distance pollen-mediated gene flow can be assumed, counteracting problems of
inbreeding depression observed under present day conditions. Thus, the mentioned
results contribute to the general assumption of extensive pollen flow in wind-
pollinated trees.
CHAPTER IV…To test for the hypothesis of effective fragment connectivity as
concluded in chapter II and III, this chapter deals with the relationships between
woodland fragment size, natural pollination and reproductive success of P. australis,
comparing natural pollination and reproduction between four different woodland
fragment sizes (three woodland fragments each, totalling twelve woodland
fragments).
The results demonstrated that while flowers collected from trees of different
fragment sizes received similar pollen loads on their stigmas, they also displayed a
tendency of having an increased percentage of pollen tubes at the top of the styles
with increasing fragment size. This finding gives reason to assume an increased
natural pollination in larger woodland fragments and can likely be explained by the
breeding system and the identity of pollen grains contained in the naturally deposited
pollen loads. However, this would be in contrast to the results of the previous
chapters indicating effective reproductive and genetic connectivity of woodland
fragments through effective pollen-mediated gene flow. Furthermore, the study also
revealed increasing progeny leaf area and biomass with increasing fragment size.
Based on these findings, it was concluded that impaired vigour of P. australis
progeny resulting from woodland fragmentation is due to inbreeding problems that
are specific to this species and/or due to decreased habitat quality in small
fragments.
CHAPTER V…This chapter analyses the influence of seed mass and seed
provenance on the germination probability of P. australis seeds. In order to conduct
the analyses, seeds from five woodland fragments distributed in two regions of the
Effects of fragmentation on pollination and regeneration of Polylepis australis 13
Córdoba mountains were collected, weighed and tested for germination and viability.
Woodland fragments differed in size, topographical position and altitude.
Results indicated a high positive correlation between germination probability and
seed mass. Thus, selecting seeds on the basis of mass is an appropriate way to
enhance germination prospects for reforestation projects. However, highest
germination probabilities were given at varying seed mass values depending on
geographical region, woodland fragment or tree identity. Therefore, it is suggested to
collect the relatively heaviest available seeds for breeding, although the absolute
seed mass of a given region, fragment or tree may be low over-all.
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Renison, D., Cingolani, A.M., Suarez, R., Menoyo, E., Coutsiers, C., Sobral, A., & Hensen, I. (2005). The restoration of degraded mountain woodlands: Effects of seed provenance and microsite characteristics on Polylepis australis seedling survival and growth in Central Argentina. Restoration Ecology, 13, 1-9.
Renison, D., Hensen, I., & Cingolani, A.M. (2004). Anthropogenic soil degradation affects seed viability in Polylepis australis mountain forests of central Argentina. Forest Ecology and Management, 196, 327-333.
Effects of fragmentation on pollination and regeneration of Polylepis australis 16
Renison, D., Hensen, I., Suarez, R., & Cingolani, A.M. (2006). Cover and growth habit of Polylepis woodlands and shrublands in the mountains of Central Argentina: human or environmental influence? Journal of Biogeography.
Reynel, C. & Leon, J. (1990). Arboles y arbustos andinos para agroforestería y conservación de suelos. Lima, Peru: Tomo II. Proyecto FAO-Holanda/DGFF.ministerio de Agricultura/FAO.
Satake, A. & Iwasa, Y. (2002). Spatially limited pollen exchange and a long-range synchronization of trees. Ecology, 83, 993-1005.
Schmidt-Lebuhn, A.N. (2005). Molecular and taxonomical studies on Minthostachys (Labiatae) and Polylepis (Rosaceae) - a contribution to the understanding of plant biodiversity in the Andes. University of Göttingen, Germany: Doctoral thesis.
Schmidt-Lebuhn, A.N., Kessler, M., & Kumar, M. (in press.). Promiscuity in the Andes: Species relationships in Polylepis (Rosaceae, Sanguisorbeae) based on AFLP and morphology. Systematic Botany.
Simpson, B.B. (1979). A revision of the Genus Polylepis (Rosaceae: Sanguisorbeae). Washington, USA: Smithsonian Institution Press.
Simpson, B.B. (1986). Speciation and Specialization of Polylepis in the Andes. In: F. Vuilleumier & M. Monasterio (Eds.), High Altitude Tropical Biogeography (pp. 304-316). Oxford, USA: Oxford University Press.
Smouse, P.E. & Sork, V.L. (2004). Measuring pollen flow in forest trees: an exposition of alternative approaches. Forest Ecology and Management, 197, 21-38.
Sork, V.J., Davis, F.W., Smouse, P.E., Apsit, V.J., Dyer, R.J., Fernandez, J.F., & Kuhn, B. (2002). Pollen movement in declining populations of California valley oak, Quercus lobata: where have all the fathers gone? Molecular Ecology, 11, 1657-1668.
Spies, T. (1998). Forest stand structure, composition, and function. In: K.A. Kohm & J.F. Franklin (Eds.), Creating a forestry for the 21st century: The science of ecosystem management (pp. 11-30). Washington, D. C., USA: Island Press.
Stacy, E.A. (2001). Cross-fertility in two tropical tree species: evidence of inbreeding depression within populations and genetic divergence among populations. American Journal of Botany, 88, 1041-1051.
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Streiff, R., Labbe, T., Bacilieri, R., Steinkellner, H., Glössl, J., & Kremer, A. (1999). Pollen dispersal inferred from paternity analysis in a mixed oak stand of Quercus robur L. and Q. petraea (Matt.) Liebl. Molecular Ecology, 8, 831-841.
Teich, I., Cingolani, A.M., Renison, D., Hensen, I., & Giorgis, M. (2005). Do domestic herbivores retard Polylepis australis woodland recovery in the mountains of Córdoba, Argentina? Forest Ecology and Management, 219, 229-241.
Troll, C. (1959). Die tropischen Gebirge. Ihre dreidimensionale klimatische und pflanzengeographische Zonierung. Bonner Geographische Abhandlungen, 25, 1-93.
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Wang, K.S. (2004). Gene flow in European beech (Fagus sylvatica L.). Genetica, 122, 105-113. Young, A., Boyle, T., & Brown, T. (1996). The population genetic consequences of habitat
fragmentation for plants. Trends in Ecology and Evolution, 11, 413-418.
Mating system, outcrossing distance effects and pollen availability in Polylepis australis 17
CHAPTER II
MATING SYSTEM, OUTCROSSING DISTANCE EFFECTS AND POLLEN AVAILABILITY IN THE WIND-POLLINATED TREELINE SPECIES POLYLEPIS AUSTRALIS
Together with A. Cocucci, D. Renison, A. Cierjacks & I. Hensen
- Basic and Applied Ecology -
Abstract
Isolation and small population size resulting from habitat destruction and fragmentation may
negatively affect plant fitness via increased levels of inbreeding and pollen limitation. However, effects
of fragmentation may vary with regard to life form and breeding system and have not been very well
studied in wind-pollinated trees. Here, we studied the effects of hand-selfing, varying outcrossing
distances of up to 30km and pollen addition on seed mass and seed germination of Polylepis australis
(Rosaceae), an anthropogenically fragmented wind-pollinated treeline species endemic to Argentina.
Furthermore, we investigated pollen germination on the stigma and pollen tube growth to determine
compatibility resulting from selfing and outcrossing, as well as pollen longevity. All hand pollinations
resulted in variable seed masses and variable seed germination across maternal trees, but selfing
reduced seed germination with significant differences between results for open pollination and
outcrosses at 30km. In addition, we found a tendency for pollen germination and pollen tube growth to
decrease following selfing. Between-fragment crosses resulted in a trend of higher reproductive output
than within-fragment crosses, whereas values were similar between open pollination and between-
fragment crosses. Our observations documented that P. australis is characterized by an exceptionally
long period of pollen viability and that, even in small fragments, pollen addition did not increase
reproductive success. Our results suggest a potential for inbreeding depression through selfing and
within-fragment crosses. However, the results also indicate that pollen flow between P. australis
woodland fragments is still effective at the current fragmentation level, counteracting negative effects
resulting from reproductive isolation.
Biparental inbreeding depression, genetic relatedness and progeny vigour in Polylepis australis 18
BIPARENTAL INBREEDING DEPRESSION, GENETIC RELATEDNESS AND PROGENY VIGOUR IN A WIND-POLLINATED TREELINE SPECIES IN ARGENTINA
Together with I. Hensen, D. Renison, K. Wesche, S. Ploch, J. Rondan Dueñas, A. Cocucci & K. Jung
- Plant Biology (submitted) -
Abstract
Background and Aims Limited gene flow and resulting spatial genetic structure are generally
considered as being the primary controlling factors in the dynamics of biparental inbreeding
depression in a wide range of plant species. However, wind-pollinated angiosperm trees have not
been adequately studied in this respect. The present study analyses the relationships between
parental genetic similarity, outcrossing distances and progeny vigour in Polylepis australis (Rosaceae),
a wind-pollinated treeline species endemic to Argentina.
Methods We investigated whether spatial genetic structuring occurs in anthropogenically
fragmented P. australis woodlands of the Córdoba Mountains. We also performed a controlled
crossing experiment using pollen collected from distances of 20m, 1km and 30km. Genetic variability
(using RAPD-PCR) and vigour (N metabolism capacity) of the resulting progeny were contrasted with
progeny from unmanipulated flowers.
Key Results We found a continuous decrease in parental genetic similarity with spatial distance
among mates and an increase both in genetic variability and N metabolism capacity in the progeny
produced from pollen at increasing distances.
Conclusions Genetic similarity between focal females and pollen donors can be seen as an
underlying factor for biparental inbreeding depression in P. australis. However, there was no difference
between N metabolism capacity resulting from open pollination and that from crosses between distant
fragments. Furthermore, the progeny resulting from long-distance crosses was closely related to that
of open pollinated progeny. On the whole, our results suggest fragment connectivity in P. australis
through effective long distance pollen-mediated gene flow with no effective inbreeding depression
problems observed under present day conditions.
Woodland fragment size, pollination efficiency and reproductive success in Polylepis australis
19
CHAPTER IV
WOODLAND FRAGMENT SIZE, POLLINATION EFFICIENCY AND REPRODUCTIVE SUCCESS IN NATURAL POPULATIONS OF WIND-POLLINATED POLYLEPIS AUSTRALIS (ROSACEAE) TREES
Together with D. Renison, A. Cocucci, I. Hensen & K. Jung
- Flora -
Abstract
It is well known that fragmentation is likely to negatively affect the reproductive success of a
species. Despite of this fact, studies on the effects of fragmentation on reproductive success in
combination with effects on natural pollination of wind-pollinated tree species are very rare. In this
study, we analyzed the relationships between woodland fragment size, natural pollination,
reproductive success and progeny vigour of the highly fragmented wind-pollinated treeline species
Polylepis australis (Rosaceae) in Argentina. We conducted our study in the high mountains of
Córdoba, comparing natural pollination and reproduction between four woodland fragment sizes.
Flowers collected from trees of the different fragment sizes received similar pollen loads on their
stigmas. Results showed a non-significant trend of increased percentages of germinated pollen grains
on the stigma and of percentages of pollen tubes reaching the styles in trees derived from larger
woodland fragments. Furthermore, our study revealed a parallel linear increase in leaf area and
biomass of 40 days old seedlings with increasing fragment size. The findings confirm that woodland
fragmentation negatively affects the vigour of P. australis progeny. Future research will need to clarify
whether impaired P. australis progeny vigour resulting from woodland fragmentation is due to
inbreeding problems specific to this species or to decreased habitat quality in small fragments.
Variation in seed mass and its effects on germination in Polylepis australis
20
CHAPTER V
VARIATION IN SEED MASS AND ITS EFFECTS ON GERMINATION IN POLYLEPIS AUSTRALIS: IMPLICATIONS FOR SEED COLLECTION
Together with I. Leyer, D. Renison & I. Hensen
- New Forests -
Abstract
South American Polylepis mountain forests are recognised as being one of the most endangered
forest ecosystems in the world. Reforestation measures have been strongly recommended but may be
hampered due to the very low seed germination reported for several Polylepis species. In order to
facilitate reforestation we analysed the influence of seed mass on germination probability for Polylepis
australis seeds in the Córdoba mountains (central Argentina). We collected seeds from 43 trees
distributed throughout 5 woodland fragments located within two regions differing in size, topographical
position, and altitude (1900 and 2200m a.s.l.). Seeds of Polylepis australis exhibited a great variation
in terms of mass and percent seed germination among individual trees and among geographical
regions. The results of logistic regression showed that germination probability was highly correlated
with seed mass. However, the explained deviance significantly increased by including the region, the
woodland fragment and especially the individual tree in addition to seed mass in the regression
models. We conclude that selecting seeds on the basis of mass is an appropriate way to enhance
germination prospects for reforestation projects. However, no absolute mass values are applicable in
this context as the highest germination probabilities were reached at varying seed mass values
depending on geographical region, woodland fragment or individual tree. We suggest collecting the
relatively heaviest available seeds, even though the absolute seed mass may be low.
Comprehensive conclusions
21
CHAPTER VI COMPREHENSIVE CONCLUSIONS
The data presented herein provide evidence for long distance pollen-mediated
gene flow rendering the wind-pollinated Polylepis australis fairly resistant to
reproductive isolation via forest fragmentation. As population connectivity and gene
flow into patches may serve to mitigate the effects of inbreeding depression
(Richards, 2000), this fact should contribute to the persistence of fragmented P.
australis woodlands.
The assumption of effective pollen flow and of genetic connectivity is underlined
by the results of low genetic differentiation of P. australis in the Córdoba mountains
and by studies on other species of this genus (Schmidt-Lebuhn et al., in press.). In
consequence, the present results should be transferable to other Polylepis species
and contribute to the general assumption of extensive pollen and gene flow in wind-
pollinated trees. Thus, previous assumptions of very limited pollen dispersal in
Polylepis, such as suggested by Graf (1986) and Fjeldså & Kessler (1996) can not be
confirmed.
However, it was also found that effective pollen movement over substantial
distances is essential for maintaining seedling fitness and, in consequence, for
natural regeneration of P. australis woodlands. To specify a precise critical minimum
distance of effective pollen flow, further investigations are necessary. Nevertheless, a
complete isolation of natural stands interrupting pollen exchange due to ongoing
Comprehensive conclusions
22
land-use practices would involve a high potential for loss of the natural reproduction
capacity of remaining fragments.
Despite of the fact that the mating system of P. australis is extraordinarily
efficient at producing highly out-bred individuals and ensuring long distance pollen-
mediated gene flow, the tendency of regressing natural pollination in trees derived
from small woodland fragments compared to larger ones indeed indicates the
beginning of a decline in the naturally deposited outcrossed pollen load in small P.
australis woodland fragments. However, the amount of compatible pollen may be still
adequate to arrive at comparable reproductive success.
In addition, the reported increase in progeny biomass and leaf area with
increasing fragment size leads to the conclusion that there are inbreeding-related
problems (e.g. Heschel & Paige, 1995; Cascante et al., 2002) but would be in
contrast to the results mentioned above indicating effective reproductive and genetic
connectivity of woodland fragments. However, a possible complementary explanation
for this finding is related to habitat quality. There are several studies suggesting that
fragmentation is more a matter of habitat degradation within small fragments
(Harrison & Bruna, 1999). Furthermore, the growing conditions of a parent plant may
influence both the number and the quality of its progeny (e.g. Weiner et al., 1997;
Gianoli & González-Teuber, 2005). In coincidence, small fragments of P. australis
can be found mostly in steep rocky areas protected from fires and livestock but
providing unfavourable growing conditions (Teich et al., 2005; Renison et al., 2006).
Considering the results presented in chapters II to IV, it becomes apparent that
even if there is genetic connectivity between isolated fragments, this connectivity can
not compensate for the loss of quantity and quality of the progeny of isolated origin
and its negative effects on the regeneration of P. australis woodlands. Although not
tested directly, considering the fact that most Polylepis woodland stands throughout
South America are also highly fragmented and degraded (Fjeldså & Kessler, 1996),
the potential of regeneration problems following fragmentation, isolation and
degradation may also be of importance for other species of the genus.
Therefore, in order to maintain progeny vigour, a clear conservation strategy is
needed to avoid further fragmentation and isolation accompanied by ongoing
degradation of Polylepis habitat throughout its entire range of distribution.
References
Comprehensive conclusions
23
Gionali, E. & Gonzáles-Teuber, M. (2005). Effect of support availability, mother plant genotype and maternal support environment on the twining vine Ipomoea purpurea. Plant Ecology, 179, 231-235.
Harrison, S. & Bruna, E. (1999). Habitat fragmentation and large-scale conservation: what do we know for sure? Ecography, 22, 225-232.
Renison, D., Hensen, I., Suarez, R., & Cingolani, A.M. (2006). Cover and growth habit of Polylepis woodlands and shrublands in the mountains of central Argentina: human or environmental influence? Journal of Biogeography.
Richards, C.M. (2000). Inbreeding depression and genetic rescue in a plant metapopulation. American Naturalist, 155, 383-394.
Schmidt-Lebuhn, A.N., Kessler, M., & Kumar, M. (in press.). Promiscuity in the Andes: Species relationships in Polylepis (Rosaceae, Sanguisorbeae) based on AFLP and morphology. Systematic Botany.
Teich, I., Cingolani, A.M., Renison, D., Hensen, I., & Giorgis, M. (2005). Do domestic herbivores retard Polylepis australis woodland recovery in the mountains of Córdoba, Argentina? Forest Ecology and Management, 219, 229-241.
Weiner, J., Martinez, S., Muller-Scharer, H., Stoll, P., & Schmid, B. (1997). How important are environmental effects in plants? A study with Centaurea maculosa. Journal of Ecology, 85, 133-142.
Anhang 24
CHAPTER VII
ANHANG
Erklärung über den persönlichen Anteil an den Publikationen Da es sich hier um eine kumulative Dissertation mit Co-Autorenschaften handelt, ist im Folgenden mein Eigenanteil an den Publikationen aufgelistet. Chapter II Seltmann, P., Cocucci, A.A., Hensen, I., & Renison, D. (submitted). Mating system, outcrossing distance effects and pollen availability in the wind-pollinated treeline species Polylepis australis (Rosaceae). Basic & Applied Ecology. Datenerhebung:
• Bestäubungsversuche, Sammeln der Blüten und Früchte: 100% • Auswiegen der Samen: 60% • Durchführung der Keimversuche: 100% • Ermittlung der Pollenlebensfähigkeit: 100% (nach Hinweisen von A. Cocucci)
Datenanalyse: 100% (nach Hinweisen von K. Wesche) Schriftliche Umsetzung: 90% (Korrekturen durch D. Renison, A. Cocucci und I. Hensen) Chapter III Seltmann, P., Hensen, I., Renison, D., Wesche, K., Ploch, S., Dueñas, R.J., Cocucci, A.A., & Jung, K. (submitted). Biparental inbreeding depression, genetic relatedness and progeny vigour in a wind-pollinated treeline species in Argentina. Annals of Botany. Datenerhebung:
• Bestäubungsversuche, Sammeln der Blüten und Früchte: 100% • Anzucht und Kultivierung der Keimlinge: 100%
Anhang 25
• Isotopenanalyse (Probenaufarbeitung, Bestimmung des N-Gehaltes nach Kjeldahl, 15N-Isotopenanalytik): 90% (Einarbeitung und Unterstützung durch K. Jung und Technische Angestellte des UFZ Leipzig)
• Sammeln des Blattmaterials für genetische Analysen: 100% • molekularbiologische Laborarbeiten durch Sebastian Ploch
Datenanalyse: • Genetische Analysen: genetische Ähnlichkeit: 100%; genetische Diversität und
genetische Distanzen: 60% (Unterstützung durch Juán Rondán Dueñas) • Analysen zur 15N-Isotopenanalytik: 100% (nach Hinweisen von K. Wesche)
Schriftliche Umsetzung: 95% (Korrekturen durch D. Renison, I. Hensen und K. Jung) Chapter IV Seltmann, P., Renison, R., Cocucci, A.A., Hensen, I., & Jung, K. (submitted). Woodland fragment size, pollination efficiency and reproductive success in natural populations of wind-pollinated Polylepis australis (Rosaceae) trees. Forest Ecology and Management. Datenerhebung:
• Sammeln von Blüten und Früchten: 100% • Pollenzählung, Ermittlung Pollenkeimung und Anteil an Pollenschläuchen mittels
Epifluoreszenzmikroskopie: 100% (nach Hinweisen von A. Cocucci) • Anzucht und Kultivierung der Keimlinge: 100% • Ermittlung der Fitnessparameter der Keimlinge (ausgenommen Isotopenanalyse):
100% • Isotopenanalyse: Probenaufarbeitung: 100%; 15N-Isotopenanalytik durch I. Flügel
vom UFZ Leipzig Datenanalyse: 100% Schriftliche Umsetzung: 97% (Korrekturen durch D. Renison, I. Hensen und K. Jung) Chapter V Seltmann, P., Leyer, I., Renison, D., & Hensen, I. (accepted). Variation in seed mass and its effects on germination in Polylepis australis: Implications for seed collection. New Forests. Datenerhebung:
• Sammeln der Samen: 100% • Auswiegen der Samen: 60% • Durchführung der Keimversuche: 100% • Durchführung der TTC-Tests: 50%
Datenanalyse: 50% (Logistische Regressionen durch I. Leyer) Schriftliche Umsetzung: 90% (Unterstützung durch I. Leyer; Korrekturen durch D. Renison und I. Hensen)
Anhang 26
Co-Autoren in alphabetischer Reihenfolge und deren Status: Cocucci, A.A., Dr. Dueñas, R.J., Dr. Hensen, I., Prof. Dr. Jung, K., Prof. Dr. Ploch, S., Student Renison, D., Prof. Dr. Wesche, K., Dr. Bestätigung des betreuenden Hochschullehrers Prof. Dr. Isabell Hensen
Anhang 27
Curriculum vitae Name: Peggy Seltmann Geburtsdatum: 25. 02. 1976 Geburtsort: Erlabrunn Ausbildung 1990 – 1994 Gymnasium Schwarzenberg
Abitur 1994 – 2000 Universität Leipzig, Fakultät für Biowissenschaften/Pharmazie und
Psychologie Studium Biologie (Diplom)
•
•
•
Schwerpunktfächer: Spezielle Botanik, Ökologie, Spezielle Zoologie, Geologie Thema der Diplomarbeit: Untersuchungen zur Ökologie der Loranthaceae und Viscaceae am Oberen Orinoco (Venezuela) Abschluss Diplom, Prädikat: sehr gut
Praktika & Kurse 10/1997 – 02/1998 La Esmeralda (Estado Amazonas, Venezuela): Canopy-Projekt der
ÖAW, Río Surumoni Botanisch-ökologisches Feldpraktikum innerhalb des Projektes „Untersuchungen zur Phänologie, Blüten- und Fruchtökologie der Bäume eines amazonischen Tieflandregenwaldes“
04/1999 – 06/1999 Umweltforschungszentrum Leipzig-Halle GmbH, Projektbereich „Naturnahe Landschaften und ländliche Räume“
Vegetationsökologisches Praktikum innerhalb der Projekte „Vorrangflächen für Naturschutz in der Bergbaufolgelandschaft Westsachsens und Nordthüringens“ und „Übertragung und Weiterentwicklung eines robusten Indikationssystems für ökologische Veränderungen in Auen“
09/2000 Namibia & Südafrika
Vegetationsökologisches Feldpraktikum innerhalb des Projektes „Evolution und Ökologie der Vegetation der afrikanischen Trockengebiete, insbesondere Analyse der Auswirkungen verschiedener Landnutzungsformen und Umweltveränderungen auf die Vegetation und den zu beobachtenden Wandel der Biodiversität“ (BIOTA – Biodiversity Monitoring Transect Analysis)
Anhang 28
11/03 Anillaco/La Rioja (Argentinien)
Workshop on Pollination Ecology Leitung: Prof. Dr. Amots Dafni (University of Haifa, Israel)
Berufserfahrung 07/1997 – 10/1998 Floristische Kartierung im Rahmen der Erstellung des
Verbreitungsatlasses der Gefäß- und Farnpflanzen Sachsens 07/2000 – 10/2000, Umweltforschungszentrum Leipzig-Halle GmbH, Projektbereich 01/2001 – 03/2001, „Naturnahe Landschaften und ländliche Räume“ 11/2001 – 03/2002 Werkverträge/Wissenschaftliche Hilfskraft innerhalb der Projekte
„Vorrangflächen für Naturschutz in der Bergbaufolgelandschaft Westsachsens und Nordthüringens“ & „Übertragung und Weiterentwicklung eines robusten Indikationssystems für ökologische Veränderungen in Auen“ (RIVA)
10/2000 – 12/2000, Universität Leipzig, Institut für Spezielle Botanik 04/2001 – 09/2001 Wissenschaftliche Hilfskraft 08/2001 – 10/2002 Landschaftsplanungsbüro Adrian, Leipzig Freie Mitarbeiterin 04/2002 – 03/2006 MLU Halle-Wittenberg, Institut für Geobotanik und Botanischer Garten
Wissenschaftliche Mitarbeiterin und Promotionskandidatin • Dozententätigkeit • Titel der Dissertation: „Effects of fragmentation on pollination
and regeneration of South American Polylepis australis woodlands“ (Kooperationsprojekt MLU Halle-Wittenberg – Nationaluniversität Córdoba, Argentinien)
02/2005 Dozent im Rahmen des internationalen Kurses: „Ökologie und
Schutz von Bergwäldern“ („Ecología y Conservación de Bosques Montanos“) in Córdoba, Argentinien
seit 04/2006 MLU Halle-Wittenberg, Institut für Geobotanik und Botanischer Garten Dozententätigkeit (Lehrauftrag)
Anhang 29
Publikationsliste Publikationen in Fachzeitschriften und Büchern Schmidt-Lebuhn, A., Seltmann, P., & Kessler, M. (in press). Consequences of the pollination
system on genetic structure and patterns of species distribution in the Andean genus Polylepis (Rosaceae): a comparative study. Plant Systematics and Evolution.
Seltmann, P. (2001). Epiphyten - Pflanzenvielfalt in den Baumkronen. Begleitheft zur Ausstellung vom 8. bis 18. März im Botanischen Garten der Universität Leipzig, Hrsg: Morawetz, W., Grau, J., & Bayer, E., Leipzig (Förderverein).
Seltmann, P., Leyer, I., Renison, D., & Hensen, I. (accepted). Variation in seed mass and its effects on germination in Polylepis australis: Implications for seed collection. New Forests.
Seltmann, P., Cocucci, A.A., Hensen, I., Renison, D. (submitted). Mating system, outcrossing distance effects and pollen availability in the wind-pollinated treeline species Polylepis australis (Rosaceae). Basic and Applied Ecology.
Seltmann, P., Hensen, I., Renison, D., Wesche, K., Ploch, S., Dueñas, R.J., Cocucci, A.A., & Jung, K. (submitted). Biparental inbreeding depression, genetic relatedness and progeny vigour in a wind-pollinated treeline species in Argentina. Annals of Botany.
Seltmann, P., Renison, D., Cocucci, A.A., Hensen, I., & Jung, K. (submitted). Woodland fragment size, pollination efficiency and reproductive success in natural populations of wind-pollinated Polylepis australis (Rosaceae) trees. Forest Ecology and Management.
Tagungsbeiträge Seltmann, P. & Morawetz, W. (2002). Mistletoes of the Upper Orinoco (Venezuela):
Infestation rates, host preferences and parasite races. Posterpräsentation. Third International Canopy Conference, Kearns, Australia.
Seltmann, P., Hensen, I., Cocucci, A.A., & Renison, D. (2003). Pollination ecology of Polylepis australis in fragmented Polylepis woodlands. Posterpräsentation. 33th Annual Conference of the Ecological Society of Germany, Switzerland and Austria (GfÖ), Halle, Germany.
Seltmann, P., Hensen, I., Cocucci, A.A., & Renison, D. (2005). Disponibilidad de polen y efectos de la distancia de cruzamiento en el éxito de la reproducción y la variabilidad genética en Polylepis australis. Vortrag. Curso y simposio de Ecología y Conservación de Bosques Montanos, Córdoba, Argentina.
Seltmann, P., Renison, D., Cocucci, A.A., Jung, K., & Hensen, I. (2005). Pollen availability and relative effects of outcrossing distances on reproductive output and genetic diversity in fragmented Polylepis australis woodlands in Argentina. Vortrag. 18th Annual Conference of the Ecological Society of Germany, Switzerland and Austria (GfÖ) – Section Plant Population Biology, Potsdam, Germany.
Anhang 30
Eigenständigkeitserklärung Hiermit erkläre ich, dass diese Arbeit bisher weder der Mathematisch-Naturwissenschaftlich-Technischen Fakultät der Martin-Luther-Universität Halle-Wittenberg noch einer anderen wissenschaftlichen Einrichtung zum Zweck der Promotion vorgelegt wurde. Ferner erkläre ich, dass ich die vorliegende Arbeit selbständig und ohne fremde Hilfe verfasst sowie keine anderen als die angegebenen Quellen und Hilfsmittel benutzt habe. Die den benutzten Werken wörtlich oder inhaltlich entnommenen Stellen wurden als solche von mir kenntlich gemacht. Ich erkläre weiterhin, dass ich mich bisher noch nie um einen Doktorgrad beworben habe. Halle/Saale, den Peggy Seltmann